static int allocate_buffers(struct cpu_hw_sf *cpuhw, struct hw_perf_event *hwc)
{
- unsigned long n_sdb, freq, factor;
+ unsigned long n_sdb, freq;
size_t sample_size;
/* Calculate sampling buffers using 4K pages
*
- * 1. Determine the sample data size which depends on the used
- * sampling functions, for example, basic-sampling or
- * basic-sampling with diagnostic-sampling.
+ * 1. The sampling size is 32 bytes for basic sampling. This size
+ * is the same for all machine types. Diagnostic
+ * sampling uses auxlilary data buffer setup which provides the
+ * memory for SDBs using linux common code auxiliary trace
+ * setup.
*
- * 2. Use the sampling frequency as input. The sampling buffer is
- * designed for almost one second. This can be adjusted through
- * the "factor" variable.
- * In any case, alloc_sampling_buffer() sets the Alert Request
+ * 2. Function alloc_sampling_buffer() sets the Alert Request
* Control indicator to trigger a measurement-alert to harvest
- * sample-data-blocks (sdb).
+ * sample-data-blocks (SDB). This is done per SDB. This
+ * measurement alert interrupt fires quick enough to handle
+ * one SDB, on very high frequency and work loads there might
+ * be 2 to 3 SBDs available for sample processing.
+ * Currently there is no need for setup alert request on every
+ * n-th page. This is counterproductive as one IRQ triggers
+ * a very high number of samples to be processed at one IRQ.
*
- * 3. Compute the number of sample-data-blocks and ensure a minimum
- * of CPUM_SF_MIN_SDB. Also ensure the upper limit does not
- * exceed a "calculated" maximum. The symbolic maximum is
- * designed for basic-sampling only and needs to be increased if
- * diagnostic-sampling is active.
- * See also the remarks for these symbolic constants.
+ * 3. Use the sampling frequency as input.
+ * Compute the number of SDBs and ensure a minimum
+ * of CPUM_SF_MIN_SDB. Depending on frequency add some more
+ * SDBs to handle a higher sampling rate.
+ * Use a minimum of CPUM_SF_MIN_SDB and allow for 100 samples
+ * (one SDB) for every 10000 HZ frequency increment.
*
* 4. Compute the number of sample-data-block-tables (SDBT) and
* ensure a minimum of CPUM_SF_MIN_SDBT (one table can manage up
*/
sample_size = sizeof(struct hws_basic_entry);
freq = sample_rate_to_freq(&cpuhw->qsi, SAMPL_RATE(hwc));
- factor = 1;
- n_sdb = DIV_ROUND_UP(freq, factor * ((PAGE_SIZE-64) / sample_size));
- if (n_sdb < CPUM_SF_MIN_SDB)
- n_sdb = CPUM_SF_MIN_SDB;
+ n_sdb = CPUM_SF_MIN_SDB + DIV_ROUND_UP(freq, 10000);
/* If there is already a sampling buffer allocated, it is very likely
* that the sampling facility is enabled too. If the event to be